Yea its compleatly ohk to use the speaker wire you already have. But I would pay attention to the gage wire the onkyo system can handle. Because if you have to thick of speaker wire it won't fit. Plus this is a 7.1 surround sound system if you don't have the 7 speaker wires in you walls your not getting full listing experience.
You can use your own..I did anyways. Just so you know I only had my subwoofer for 2 days. Its been months now and its not fixed. The sub is really crappy. It broke twice. I just bought a energy sub and the system now rocks. Just thought you would like to know.
we bought new speaker wire because we didn't get any with our system. I would buy more because I think we used 100 feet of speaker wire in the basement, for this system. What you have may not be enough.
Im sure that the speaker wires in your walls are of better quality than the ones that are supplied with the unit. usually the ones they send with the unit with what you would call starter wires. i always upgrade my wires with at least 16 gauge name brand wires . Such as monster cable.